In Ohio, what is the maximum time that a prison can keep an inmate in segregation? I thought I heard it is up to 90 days. I know they can get released earlier if the space is needed in the hole for new offenders, but wasn't sure if there was a maximum amount of time or is it at the whim of the warden or investigator?

Pelican Bay was the site of a Cruel and Unusual suit by prisoners of the Secure Housing Unit against the prison. There was a finding that isolation is cruel and unusual, as it exacerbates any underlying mental conditions. Still, when balanced against the facility's interest in security and keep inmates alive, the facility's interest wins, for the most part. Arguably, such isolation practices have to be mitigated with some contact with other humans, attention to mental health issues, and some chance of eventually working your way off that sort of restriction.

On a practical level, they can keep you there indefinitely. There are units throughout the US, both state a federal, where inmates are kept for life.

Sorry, but that's how it is right now. Might want to check with the ACLU and prisoner rights organizations as this issue is still being litigated. Won't get you out of "the hole", but it will help you put your anger at the system into a place where it might do others some good.